meson: remove unused stdin_wrapper.py script

Not needed any more. Used to be used with fc-case and fc-lang,
but those have since been rewritten in python.
10 jobs for meson-remove-unused-stdinwrapper-script in 7 minutes and 34 seconds (queued for 3 seconds)
Status Job ID Name Coverage
  Build
passed #6507249
gst-macos-10.15
meson macos

00:03:51

passed #6507246
meson-mingw-w64-build

00:05:38

manual #6507250
docker windows 1809 allowed to fail manual
meson msys2
passed #6507244
meson-shared-build

00:02:55

passed #6507245
meson-static-build

00:04:33

passed #6507247
docker windows 1809
meson vs2017 amd64

00:01:27

passed #6507248
docker windows 1809
meson vs2017 x86

00:01:20

passed #6507243
mingw-build

00:06:04

passed #6507241
shared-build

00:07:34

passed #6507242
static-build

00:06:49